FPC exitcode 201 while using ansistring. String does not do that

Question

I have a question. I wrote this little program and it was working perfectly, until I changed s and s2 from string to ansistring. I need to use ansistring, because it will be way longer than 255 characters. Thanks for your response.

    {$H+}
program Test;
uses Crt;
var s,s2:string;
    konec,radek:boolean;
    i,a,z:integer;
begin
  ClrScr;
  s:='';
  s2:='';
  i:=0;
  a:=0;
  z:=1;
  konec:=false;
  radek:=false;
  repeat
    s2:='';
    readln(s2);
    s:=s+s2;
  until s2='';
  while konec=false do begin
    while radek=false do begin
      a:=a+1;
      if length(s)+1=a then begin
        radek:=true;
        s:='';
        if a<60 then writeln(s2);   
      end;
      if not (a=length(s)+1) then begin
      if s[a]=' ' then
        i:=a;
      s2:=s2+s[a];
      if not (s[a]=' ') then
      if a=60 then begin
        radek:=true;
        delete(s2,i,60-i+1);
        writeln(s2);
        s2:='';
        delete(s,z,i);
      end;
      if (s[a]=' ') and (a=60) then begin
        radek:=true;
    writeln(s2);
    s2:='';
    delete(s,z,i);
      end;
      end;
    end;
    radek:=false;
    a:=0;
    if (s='') then konec:=true;
  end;
  readkey;
end.

Answer 1

The core thing to know is that shortstring often has no problem with out of bounds string access (s[a] when a is not in the allowed range (a>=1) and (a<=length(s)) )

You set S to '' in this code:

 if length(s)+1=a then begin
    radek:=true;
    s:='';
    if a<60 then writeln(s2);   
  end;

but you don't reset "a". So the following condition is true and the s[a] access bombs out.

  if not (a=length(s)+1) then begin
  if s[a]=' ' then
    i:=a;

How to solve this is left as an exercise to the reader.

Learn to use range checks and you find issues like this in a minute (hint add -Cr -gl to the commandline)